In the past, power drills have been used to produce holes in a workpiece. Also, in the past accessories known as nosepieces have been used with power drills to fasten the drill into a drill jig or similar positioning device so that a hole produced would be properly positioned on the workpiece. Also, nosepieces served to protect the drill bit from damage and to provide a conduit to carry coolant to the drill bit or other cutting tool and to the point on the workpiece being drilled.
In the past, however, when it was necessary to change the length of the drill bit being used, a specific nosepiece was required because there was no nosepiece with an adjustable length dimension available. Thus, it was necessary to keep a tool inventory which included a nosepiece for each drill bit length.
Additionally, the radial relationship between the nosepiece coolant port and the workpiece being drilled could only be changed by disassembling the drill and nosepiece and reassembling them by shimming between nosepiece and power drill to achieve correct positioning of coolant port position with respect to workpiece. Shimming process is continued until proper positioning is achieved. This requires that an inventory of specially designed shims be carried. Such a method is time consuming and costly because of the large tool inventory required for each drill and drill bit, especially when changing the drill bits after drilling every few holes.
Furthermore, changing nosepieces was itself a time consuming process requiring the unscrewing of the nosepiece to be removed and the screwing on of the nosepiece required for a particular job.
Past efforts made in regards to an adjustable nosepiece utilize a threaded drill motor over which the threaded bore of the nosepiece is engaged. For instance, U.S. Pat. No. 4,538,943 issued to Clifton, et al., describes such a device and also having a locking means whereby the nosepiece may be locked into a predetermined position during each rotation of the nosepiece relative to the drill motor body. This provides a rough linear adjustability for the nosepiece that is dependent on the fineness of the threaded bore.
U.S. Pat. No. 4,588,334, issued to Khurana, the inventor of this application, provides for a clocking mechanism for locking the nosepiece in a predetermined position relative to the drill motor body. The clocking mechanism of U.S. Pat. No. 4,588,334 provides for a much finer adjustment of the nosepiece, both in the linear and in the rotational directions. Depending on the number of teeth in the U.S. Pat. No. 4,588,334 device, the incremental linear adjustability has been decreased by a factor of approximately 20 from that of the Clifton device.
An attendant problem persists with these prior art devices, however, in that if the nosepiece requires an adjustment of a length greater than the threaded length of the nosepiece bore, the complete nose-piece mechanism requires removal and replacement with a nose-piece of suitable length. This problem may arise when the drill bit requires replacement with a much shorter or longer drill bit, but also because of other considerations. The replacement of the nosepiece mechanism in the prior art devices remains a lengthy and tedious process whereby the nosepiece is completely unscrewed from the drill motor body. Thus, it can be readily seen that the prior art nosepiece accessories available for use with power drills do not deal with the problem of linear adjustability of relatively large dimensions.